Medication dosage calculator for healthcare workers and parents. Calculates dose by body weight, BSA, and IV drip rate.
Four tabs: weight-based dose (mg/kg), BSA-based dose (mg/m²), IV drip rate (macro / micro drip), and dosage unit conversion (mg, mcg, g, mL).
Disclaimer: Always confirm with a physician or pharmacist. For education and reference only — not a substitute for clinical judgment.
Calculator information
📋 How to use this calculator
- Choose the calculation method: weight-based dosing (mg/kg), BSA-based dosing (Body Surface Area, mg/m^2), IV drip rate, or unit conversion.
- For weight-based dosing, enter patient weight (kg), the prescribed dose (mg/kg/dose), and dosing frequency (per day).
- For BSA, enter height (cm) and weight (kg) - the calculator computes BSA automatically using the Mosteller or Du Bois formula.
- For IV drip rates, enter fluid volume (mL), infusion duration (minutes/hours), and the drop factor of the IV set (macrodrip 15-20 gtt/mL or microdrip 60 gtt/mL).
- Click Calculate to see dose per administration, total daily dose, the number of tablets or mL needed, and the drip rate.
- Tip: always verify with a pharmacist or physician. This calculator is a decision-support tool, not a substitute for clinical supervision.
🧮 Drug dosing and IV drip rate formulas
Dose_BW = dose_per_kg x weight_kg | BSA Mosteller = sqrt((height_cm x weight_kg) / 3600) | BSA Du Bois = 0.007184 x height^0.725 x weight^0.425 | Dose_BSA = dose_per_m2 x BSA | Drops/min = (Volume_mL x Drop_factor) / Time_min | mL/hr = Volume_mL / Hours
- dose_per_kg = prescribed dose (mg/kg/dose)
- weight_kg = patient body weight (kg)
- height_cm = patient height (cm)
- BSA = Body Surface Area (m^2); adult average is about 1.7 m^2
- Drop_factor = 15 or 20 (macrodrip) or 60 (microdrip) gtt/mL
- Volume_mL = total infusion fluid volume
- Time_min = infusion duration in minutes
The Mosteller BSA formula is most widely used because it is simple. Pediatric dosing usually uses mg/kg, while chemotherapy and certain specialty drugs use mg/m^2 BSA. Always verify maximum daily dose and contraindications.
💡 Worked example: 5-year-old child, 18 kg, needs acetaminophen 15 mg/kg every 6 hours and 500 mL NaCl IV over 8 hours
Given:- Body weight: 18 kg
- Acetaminophen dose: 15 mg/kg/dose every 6 hours (4x/day)
- Available syrup: 120 mg/5 mL
- 500 mL NaCl IV over 8 hours, macrodrip set 20 gtt/mL
Steps:- Acetaminophen dose per administration: 15 mg/kg x 18 kg = 270 mg
- Syrup volume per dose: (270 mg / 120 mg) x 5 mL = 11.25 mL (round to 11 mL)
- Daily dose: 270 mg x 4 = 1,080 mg (at the 60 mg/kg/day maximum of 1,080 mg)
- Drip rate: (500 mL x 20 gtt) / (8 x 60 min) = 10,000 / 480 = 20.83 gtt/min (round to 21 gtt/min)
- Rate in mL/hr: 500 / 8 = 62.5 mL/hr
Result: Acetaminophen 11 mL of syrup every 6 hours (1,080 mg/day, right at the daily ceiling). NaCl infusion at 21 gtt/min or 62.5 mL/hr.
❓ Frequently asked questions
Why are pediatric doses calculated per kilogram of body weight?
Children have different drug metabolism and distribution than adults, so doses must be scaled to body size to avoid underdosing (ineffective) or overdosing (toxic). Weight-based mg/kg dosing produces an optimal and safe blood concentration. Some drugs - notably chemotherapy and systemic steroids - use BSA (mg/m^2) because it better captures volume of distribution in children.
What is the difference between macrodrip and microdrip sets?
Macrodrip IV sets deliver 15 or 20 drops per mL (20 gtt/mL is most common) and are used for adult fluids at high volumes and rates. Microdrip sets deliver 60 drops per mL and are used for pediatrics, neonates, and drugs requiring high precision at slow rates. Always confirm the drop factor printed on the IV tubing packaging.
How do I calculate BSA accurately?
BSA can be calculated with several formulas: Mosteller (most popular, BSA = sqrt(height x weight / 3600)), Du Bois (classic, BSA = 0.007184 x height^0.725 x weight^0.425), or Haycock (for children). Mosteller is the most practical and accurate for adults; Haycock is more accurate for children under 30 kg. Average adult BSA is 1.6-2.0 m^2. BSA is used for chemotherapy, systemic corticosteroids, and certain antibiotics.
What should I do if I miss a dose?
General rule: if you remember within a few hours of the scheduled time, take it as soon as possible; if it is almost time for the next dose, skip the missed one and resume the regular schedule. Do NOT double up to make up for the missed dose. For drugs with narrow therapeutic windows - anticonvulsants, anticoagulants, insulin - call your pharmacist or physician. A reminder app or weekly pill organizer helps prevent missed doses.
How do I convert a drug from mg to mL or tablets?
For syrups: Volume_mL = (desired_dose_mg / strength_mg) x strength_volume_mL. Example: acetaminophen 250 mg from a 120 mg/5 mL syrup = (250/120) x 5 = 10.4 mL. For tablets: tablets = desired_dose / strength_per_tablet. Example: amoxicillin 500 mg from 250 mg tablets = 2 tablets. For parenteral drugs, check the reconstituted vial concentration (mg/mL after dilution) and required diluent volume.
📚 Sources & references
Last updated: May 11, 2026